1. Field of the Invention
The present invention is generally related to a data analysis method, apparatus and article of manufacture and more particularly to an apparatus, article of manufacture and analysis method for measuring and analyzing vibrations and identifying failure signatures in the vibrations.
2. Background Description
System efficiency is a measure of the energy expended in performing a task with respect to the energy consumed by the system to perform the task. Energy may be lost, for example, thermally (e.g., as heat), optically (e.g., as light) or mechanically (e.g., as vibrations). Besides dissipating energy to reduce efficiency, vibrations can stress a structure to the point of failure. Thus, designers commonly resort to various design methods to reduce and minimize vibration. However, system dynamics may cause vibration, i.e., where time varying forces induce system vibrations. Consequently, structural vibrations can never be totally avoided or eliminated.
The renowned Tacoma Narrow Suspension Bridge is one well-known example of deleterious vibrations in a structure. Wind caused the bridge to vibrate at resonance. During a period of sustained high wind, the wind re-enforced the resonant vibrations. The bridge oscillation magnitude continually increased until a structural failure occurred and the bridge collapsed. Although most bridges sway in the wind to some extent, most do not collapse from the swaying. Unfortunately, no one had any idea that wind would cause the collapse of Tacoma Narrow Suspension Bridge. Otherwise, officials could have taken steps to address that instability, e.g., introduce members to change the resonant frequency or, at least, to dampen the vibrations that caused the bridge to sway.
So, while vibrations may be unavoidable, monitoring and analyzing vibrations, whether in the overall system or in a single structural member, can provide valuable insight and additional information regarding the dynamic characteristics of the structure/system. Every structural member has a natural resonant frequency that is related in part to its stiffness. Typically, material stiffness changes just prior to failing. For example, when bending a wire back and forth, one may notice that the wire gets softer just before it breaks. So, since one may determine changes in stiffness by measuring vibration frequency, measuring vibration frequency has proven to be one valuable indication for non-destructive health monitoring. The time-frequency distribution of vibrations in machinery as well as in static structures also have been analyzed to determine structural damping characteristics with respect to system dynamics.
Though a number of approaches are available for studying structural vibrations, unfortunately, those approaches do not separate stabilizing, dampening vibrations from de-stabilizing vibrations or vibrations that indicate instability. Further, those approaches typically, do not provide consistently reliable dampening predictor indications.
In particular, it is important to understand vibrational instability in modern airborne structures. State of the art aircraft materials and aircraft construction methods have led to structures that are lighter in weight but also are reduced in stiffness. Consequently, these aero-elastic design materials have such reduced stiffness that the resulting structures are susceptible to structural dynamics problems, specifically the onset of instability. Unfortunately, adequate tools are unavailable to predict stability margins for these structures, especially, tools applicable to understanding structural dynamic instabilities such as flutter. It is critical to flight safety in particular to have valid flight flutter prediction techniques that can determine the onset of instability in aero-elastic structures from the flight data.
Thus, there is a need for tools that reliably predict stability margins in aero-elastic structures applicable to structural dynamic instabilities such as flutter.